1. Field of the Invention
This invention relates to a folding device built into or appended to a web-fed printing press, as in newspaper production, for giving a down-the-middle fold to a web or webs of printed paper, cutting the web or webs into sections, and folding the successive paper sections across the middle into the form of signatures. More particularly, the invention deals, in the folding device of the rotary printing press, with a jaw cylinder having one or more jaw cavities formed in its surface parallel to the cylinder axis for receiving the midpart of each paper section to be folded.
2. Description of the Prior Art
Japanese Unexamined Patent Publication No. 63-189367 is hereby cited as showing the typical construction of the folding station of a web-fed printing press. Mounted parallel to one another at the folding station are a cutting cylinder, a folding cylinder and a jaw cylinder, all in constant rotation at the same circumferential velocity during the progress of printing. The printed web or webs of paper are first wrapped around part of the folding cylinder and, while traveling thereover, cut into successive sections by cutting blades on the cutting cylinder which is held against the folding cylinder via the web or webs. The cutting blades cut the web or webs by being engaged in grooved anvils or beds on the folding cylinder. Each paper section subsequently travels over the folding cylinder by having its leading edge pierced by a series of retractable pins on the surface of the folding cylinder.
The folding cylinder is additionally equipped with elongate folding blades each extending parallel to the folding cylinder axis and arranged at circumferential spacings thereon. Each folding blade is movable radially of the folding cylinder for pushing the paper section into one of the elongate jaw cavities which are formed in the surface of the jaw cylinder at constant circumferential spacings.
Pushed off the surface of the folding cylinder by one of the folding blades, the paper section has its midpart placed between a fixed and a movable jaw in one jaw cavity. The midpart of the paper section is then captured, together with the folding blade, between the fixed and movable jaws as the movable jaw is closed against the fixed jaw. The paper section is subsequently carried away from the surface of the folding cylinder by the jaw cylinder as these cylinders continue rotation in opposite directions. The folding blade withdraws from between the folds of the midpart of the paper section, leaving the same sandwiched between the fixed and the movable jaw thereby to be creased. The paper section is subsequently folded along the centerline as the leading half of the paper section is doubled over its trailing half while being carried away from the folding cylinder onto the jaw cylinder.
There has been a problem left unsolved in conjunction with the engagement of the paper section between each set of fixed and movable jaws on the jaw cylinder. The paper section has its midpart held caught between the fixed and the movable while being transferred from the folding to the jaw cylinder and doubled over itself, until it is carried by the jaw cylinder to the preassigned angular position from which the folded paper section is deposited on a delivery conveyor. Considerable frictional resistance is exerted on the paper section as the latter is pulled off the surface of the folding cylinder onto the jaw cylinder. The jaws are required to grip the paper section against the risk of accidental disengagement in the face of such frictional resistance.
The paper sections are literally fresh from the press, however. Ink offset has been easy to occur between the contacting surfaces of each paper section when the same is caught strongly by the jaws, and particularly when the folding blade is being withdrawn from the folds of the paper section. This is because the folding blade rubs hard against the paper sections, behaving as if prying open the jaws, as it withdraws from between the jaws by the rotation of the jaw cylinder and folding cylinder in opposite directions. The ink offset must be avoided by any means as it represents a serious impairment of printing quality and a degradation of the commercial values of the printings.
The present invention seeks to make it unnecessary for the paper sections to be bitten by the jaws so hard as to cause ink offset between their contacting surfaces and, at the same time, to preclude the likelihood of the paper sections accidentally falling off the jaw cylinder while being folded thereon.
Stated briefly, the invention concerns a folding station downstream of one or more printing stations of a web-fed printing press. The folding station is such that a web of printed paper or two or more such webs in superposition are cut into sections by a cutting cylinder while traveling on a folding cylinder. Each paper section has its midpart subsequently pushed off the folding cylinder into a jaw cavity in a jaw cylinder in order to be folded into a signature while being transferred from the folding cylinder onto the jaw cylinder.
More specifically, the invention deals with the jaw cylinder comprising a pair of hooks mounted adjacent the opposite ends of the jaw cavity in the jaw cylinder for movement into and out of a space created by the midpart of each paper section upon insertion in the jaw cavity. The hooks are driven by hook drive means to enter the space bounded by the midpart of each paper section when the same is inserted in the jaw cavity, and to withdraw from the space after the paper section has been folded on the jaw cylinder.
In a preferred embodiment of the invention to be disclosed herein, the hooks are each driven into and out of hooking engagement with the inserted midpart of each paper section by a cam of arcuate or annular shape affixed to the frame means to which the jaw cylinder is rotatably mounted. The hook drive cams are contoured to time the operation of the hooks to the insertion and withdrawal of the midpart of the paper section into and out of the jaw cavity in the jaw cylinder. The paper section can therefore be held positively retained in the jaw cavity against the risk of accidental disengagement while being folded. The hooks will not cause ink offset between the contacting surfaces of the paper section as they mostly engage the margins of the printings.
The provision of a fixed and a movable jaw in the jaw cavity in the jaw cylinder, as in the prior art, is nevertheless preferable from the stand-point of creation of a well-defined fold on each paper section. A creation of neat folds is desirable to expedite the subsequent processing of the paper sections or signatures. Such jaws, however, may be pressurized only to an extent necessary for folding rather than for retaining the paper section against detachment. Ink offset is therefore not to be caused by the jaws, either.
The above and other objects, features and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiments of the invention.